1. Field of the Invention
This invention relates to a control system for a parts feeder, and more particularly to a system for controlling the feed rate of parts delivered by the parts feeder which feeds various kinds of parts to an assembling machine or the like by vibrating tile parts at a predetermined frequency.
2. Description of the Prior Art
Heretofore, various kinds of vibrating type parts feeders are known in the art. For example, published Japanese Utility Model Application, KOKAI (Early Publication) No. SHO 59-68715 discloses a parts feeder which comprises a bowl provided with a side wall having a spiral passage formed on the inner peripheral surface thereof in the form of a gently upwardly sloping surface and an electromagnet disposed beneath the bowl, the bowl being adapted to accommodate a large number of parts, the arrangement being made such that then the bowl is vibrated by the action of the electromagnet, the parts within the bowl are transferred along the passage and delivered in turn while they are being vibrated by the vibration of the bowl.
As for the system for controlling the driving of such a parts feeder, for example, published Japanese Patent Application, KOKAI No. SHO 57-27808 proposes a system wherein a light projector and a receptor of a photoelectric conversion device are disposed on a straight line so as to pass light beams through the clearance between a fixed core of an electromagnet disposed beneath the bowl and a movable core fixedly secured to the bowl, the arrangement being made such that the change in the amount of light passing through the above-mentioned clearance due to changes in the amplitude of vibration of the movable core is converted into a value of electric current to detect the amplitude of vibration of the bowl, and the amplitude of vibration of the bowl thus obtained is fed back to an amplitude controlling circuit so as to control an electric current supplied to the electromagnet for driving the bowl, thereby driving the bowl always with a predetermined amplitude. Further, there has so far been used a parts feeder provided with a photoelectric switch attached to a parts delivery chute disposed on the side of outlet for tile parts so that the photoelectric switch may detect whether the parts delivered by a bowl are overstocked in the chute or not.
In the above-mentioned conventional control system, since the object to be controlled is the bowl for delivering the parts by vibrating them and the feed rate of the parts is not grasped and controlled, there is a problem in that changes in the feed rate of parts occurs depending on the amount of the parts accommodated in the bowl. That is to say, even if the vibration of the bowl is controlled to a prescribed amplitude, the feed rate of the parts changes because the proper value of the amplitude for ensuring a desired feed rate varies with the number of the parts accommodated in the bowl. In addition, since the actual feed rate of the parts is unknown, if the consumption of the parts by the assembling machine is out of balance to the supply of the parts by the parts feeder at the time of initial setting, shortage in supply of the parts to the assembling machine takes place even if the amplitude of vibration of the bowl is kept constant. Further, another problem is that since the proper value of amplitude differs with every parts feeder, in case the parts feeder is replaced with a new one, the vibration of the bowl must be reset to a proper amplitude to ensure a desired feed rate of the parts.